Capacitors such as supercapacitors (also known as ultracapacitors) have found increasing use in electric vehicles and the like, using a charge-discharge process that provides electrical-powered vehicles with an energy-saving and environmentally-friendly solution. They also can be used in related technologies for electric-powered devices.
With continued urbanization, awareness of the need for environmental protection also has increased. As part of urban transportation, vehicles powered by chemical batteries are widely used because they create less pollution than vehicles powered by internal combustion. Because supercapacitors have electrical storage capacities of many Farads, they have been used successfully in electric vehicles, hybrid vehicles, and the like. In many electric vehicles, the electrochemical supercapacitors that are used as a power supply are asymmetrical in structural design. The anode and cathode of the supercapacitor are made of different materials. For example, the anode of the supercapacitor may be made of metal oxides, while the cathode of the supercapacitor may be made of activated carbon materials. For such a supercapacitor, on the one hand, the use of an anode of secondary batteries, such as a nickel hydroxide electrode, ensures that the supercapacitor has a high energy density (energy per unit weight). On the other hand, the use of a double-layer cathode (carbon) of ultra-long life cycle (cycles>105), can enable such supercapacitors to sustain a long-term life of as much as 8-10 years.
A supercapacitor includes an anode, a cathode, an electrolyte, a membrane, and other components. Supercapacitor membranes play a vital role in the performance of supercapacitors. The membranes separate the anode and cathode to prevent direct electrical conduction, while also allowing ions to move freely through the membrane to form a current loop cycle or circuit. In addition, the membrane also has to provide good hydrophilic performance, liquid absorption capacity, air permeability, a sufficient degree of mechanical strength, and anti-chemical and electrochemical corrosion properties. Currently, supercapacitors use a variety of different membranes to provide these properties.
Asymmetrical supercapacitors for electric vehicles, hybrid power vehicles, and other applications are usually designed to work in over-charge/discharge mode to maximize the system's energy density. However, a consequence of operating in a long-term over-charge/discharge mode is an increase in internal pressure caused by the internal accumulation of hydrogen and oxygen gas produced by the supercapacitors. The increased pressure results in the safety valve of the supercapacitor remaining open all the time. The problem this condition creates is that (1) the supercapacitor system can only be used in a valve-regulated mode, which requires electrolytes to be added on a regular basis so that the supercapacitor cannot be used maintenance-free, and (2) the long-term over-charge/discharge state accelerates the degradation of the activated material in the supercapacitor anode, reducing the life cycle of the supercapacitor. During operation, a large volume of gases accumulates at the positive and negative electrodes around the supercapacitor membrane, thereby reducing the efficiency of the supercapacitor. Although this situation creates favorable conditions for combining the hydrogen and oxygen gas to reduce the internal pressure, known membranes are not able to catalyze or otherwise promote the combination of hydrogen and oxygen.
Accordingly, a process is needed that can cause the accumulated hydrogen and oxygen in a supercapacitor to combine to form water, thereby reducing the pressure in the supercapacitor and increasing supercapacitor efficiency.